The invention relates to a method for producing a semi-finished product to be made into a CFRP component (carbon-fiber reinforced component). The invention relates, in particular, to a continuous method for producing a CFRP component in which the production of a regrind semi-finished product is one intermediate step.
In the prior art, it is known how to subject plastics to a regrind process in order to recycle them in a subsequent reprocessing process. Thus, e.g., a method is disclosed in DE 19710098 A1 for producing polyethylene terephthalate (PET) regrind from flakes, as well as a PET product produced by the method. PET products find multiple uses, for example as bottles, qualified films and fibers, medical devices, especially medical syringes and medical containers. One tries to utilize the products as much as possible in the material cycle. However, a major problem here is that the quality of the products changes with an increasing proportion of PET regrind.
Molded parts of polymer materials, which are used in particular in motor vehicle interiors, need to meet high mechanical and environmental requirements and, in particular, they must satisfy requirements in terms of their mechanical properties, their surface properties, their aging as well as their odor and emission behavior. It is known how to use various polymer materials for the manufacture of components and molded parts for motor vehicle interiors. A typically used material is a fiberglass-reinforced ABS/PC material (polymer blend of acrylic-butadiene/styrene copolymer and polycarbonate). However, this material has insufficient UV stability, poor flowing behavior, a poor thermal aging behavior (toughness and elongation at break following hot storage) and unfavorable surface properties, as well as poor foam adhesion and, in particular, a poor odor behavior. By odor behavior of plastics is meant the tendency for the parts to give off volatile components which can be perceived by a person after climate testing and especially a temperature exposure of fixed duration and fixed temperature.
Moreover, it is known in the prior art how to use fiber-reinforced molded plastics for mechanically stable components and molded parts. The reinforcement fibers used in the manufacture of structural parts are, for example, glass fibers, natural fibers or carbon fibers and fillers. However, fiber materials such as glass fibers are expensive. Another drawback of glass fibers is that they are relatively heavy.
Extrusion, co-extrusion and pultrusion methods are used in the prior art for the manufacture of components such as vehicle parts and vehicle interior parts, for example, especially in the manufacture of profiles. However, the high costs still remain a limiting factor. The manufacture of carbon fiber-reinforced components with such methods is therefore significantly influenced by the material costs and the quantity of fibers used. Moreover, it is known how to use carbon fiber scrap during manufacturing, especially during the manufacturing of fleeces, in order to lower the costs. But the processing methods known in the prior art are limited by discontinuous methods. Thus, each time definite batch amounts are processed in the discontinuous process.
It is therefore desirable to provide a production method which works continuously and with which larger quantities of duroplastics or thermoplastics can be processed.
Therefore, the problem which the present invention proposes to solve is to overcome the aforementioned drawbacks and, in particular, to provide a continuous method with short process times which enables an economical production of semi-finished products and components of polymer materials with good final mechanical properties.
This problem is solved by a method for manufacturing a semi-finished product in a continuous process to be made into a carbon fiber-reinforced component, wherein the method includes the following steps: a. feeding carbon fiber scrap into an extruder; b. adding a plastic polymer to the extruder; c. pulverizing the carbon fiber scrap and blending the pulverized scrap with the plastic polymer to form a polymer mass; and d. impregnating the polymer mass with a resin in order to form a regrind prepreg from it, which is given suitable forms and/or lengths.
The basic notion of the invention is to feed suitable carbon fiber scrap together with a plastic polymer to a pulverizer and extruder in order to generate from this a carbon fiber polymer mass and to impregnate the polymer mass in a resin. From this one obtains a regrind prepreg, which is placed in suitable shapes and/or given suitable lengths. These regrind prepregs can then be given an approximately final form in an additional sub-step by way of extrusion processes.
An extrusion, co-extrusion or pultrusion method or the like can be used for this in order to make molded parts such as profiles or vehicle interior parts.
In a general form of the invention, therefore, a method is provided for the manufacture of a semi-finished product in a continuous process for processing into a carbon fiber-reinforced component with at least the following steps:                feeding of carbon fiber scrap into an extruder;        adding of a plastic polymer to the extruder;        pulverization of the carbon fiber scrap and blending of the pulverized scrap with the plastic polymer to form a polymer mass;        impregnating of the polymer mass with a resin in order to form a regrind prepreg from it, which regrind prepreg is placed in suitable forms and/or lengths.        
Accordingly, one aspect of the invention consists in mechanically pulverizing carbon fiber-reinforced plastic scrap or carbon fiber-reinforced plastic materials in an extruder, so that a carbon fiber regrind is produced therefrom, and then to blend this with a duroplastic or thermoplastic in a desired mix ratio to form a polymer mass. The mix ratio and the carbon fiber scrap size has an influence on the desired mechanical and technical properties of the later molded part. The degree of pulverization can preferably be adjusted by way of the screw geometry or the screw length of the extruder.
Preferably, a method is proposed in which either a thermoplastic or a duroplastic is used as the plastic polymer.
In an especially preferred embodiment of the invention, the pulverization of carbon fiber scrap or carbon fiber waste fed into the extruder occurs directly in the extruder. In this way, a cost-intensive prepulverization and thus a separate process step can be avoided. In one preferred embodiment, accordingly, an extruder is used for the pulverization of the carbon fiber scrap that has a screw geometry adapted to the desired degree of pulverization. The degree of pulverization can be adjusted, for example, in terms of the screw length or the shape of the screw geometry.
Alternatively, a pulverization device can also be arranged in the extruder so that when the extruder screw is activated the pulverization occurs at the same time via the pulverization device.
In one preferred embodiment of the invention, the extruded polymer mass is impregnated with a resin in order to form a regrind prepreg from this, which can be placed in suitable forms and/or lengths. Moreover, it is accordingly preferred in a sub-step following the extrusion to cut the regrind prepreg to length at defined intervals after leaving the extruder, i.e., to cut suitable prepreg pieces for further processing. Alternatively, the regrind prepreg after leaving the extruder can also be placed in a defined form.
In another preferred embodiment of the invention it is provided that the regrind prepreg cut to length or placed in form is reshaped into an approximately final semi-finished product by way of pressure shaping, such as extrusion in a die.
It is especially advantageous for the regrind prepreg to be fed to a shaping cavity of a pressing die for the pressure shaping and to be pressed by way of a pressing punch. According to the invention, the aforementioned sub-steps can be connected in a continuous conveyor belt process or connected in series in a production line.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.